Diesel dosing unit having an anti-coking injector assembly, and methods of constructing and utilizing same

ABSTRACT

A diesel dosing unit (DDU) is disclosed, having a fluid injector assembly. The fluid injector assembly includes a fluid injector and an attachment assembly attached to a downstream end of the fluid injector, the attachment assembly at least partly defining a fluid path in fluid communication with a fluid path of the fluid injector. The DDU further includes a DDU housing in which the injector assembly is disposed, the DDU housing being configured to directly attach to an exhaust pipe of a vehicle. The fluid injector assembly is dimensioned to largely match the dimensions of an existing injector of a reductant delivery unit (RDU) such that the DDU housing utilizes the housing of the existing RDU.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. provisional application 62/595,358, filed Dec. 6, 2017, and entitled “A Diesel Dosing Unit Having an Anti-Coking Injector Assembly, and Methods of Constructing and Utilizing Same,” the content of which is hereby incorporated by reference herein in its entirety. The present application is related to U.S. nonprovisional application Ser. No. 15/833,683, filed Dec. 6, 2017, and titled, “Anti-Coking Injector Assembly for a Diesel Dosing Unit, and Methods of Constructing and Utilizing Same,” the content of which is incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to an attachment to a fuel injector for creating a unitary, outward opening injector assembly which combines with a housing for a reductant delivery unit for use in a diesel dosing system.

BACKGROUND

In a diesel engine, exhaust gas temperature management is critical for meeting emissions requirements. One method of exhaust gas temperature management is known as “post-injection” which utilizes an additional injection of fuel from the in-cylinder fuel injector during the exhaust stroke. Post-injection is known to cause oil dilution and requires more frequent engine maintenance. Another method of exhaust gas temperature management is a dedicated system that injects fuel directly into the exhaust stream. In particular, diesel fuel is delivered or otherwise sprayed into the exhaust stream in front of a diesel oxidation catalyst in order to provide the thermal energy required to re-burn captured particulates at the diesel particulate filter or to thermally manage the exhaust system temperature conditions. The delivery device is referred to as a diesel dosing unit (DDU). Because dedicated systems for performing these methods are on-demand, there may be extended periods of inactivity. Extended periods of high temperature and inactivity have been seen to cause the DDU injector to be stuck in the closed position. This leads to complicated injector designs, including remotely mounting DDU injectors from the diesel engine exhaust pipe and/or complex thermal isolation of the DDU injector.

SUMMARY

Example embodiments are directed to a DDU that is robust, simple in design and inexpensive to manufacture. In an example embodiment, the DDU includes a fuel injector including a first housing, a fluid inlet disposed at a first end of the first housing for receiving fluid, a fluid outlet disposed at a second end of the first housing for exiting fluid from the first housing, the first housing defining at least in part a fluid path through the first housing between the fluid inlet and the fluid outlet. The fuel injector further includes an actuator unit and a valve assembly operably coupled thereto for selectively discharging fluid in the fluid path from the fluid outlet when the valve assembly is in an open state and for preventing fluid in the fluid path from exiting the fluid outlet when the valve assembly is in a closed state. The DDU also includes an attachment assembly having a second housing or body with a first end attached or attachable to the second end of the first housing and a second end. The second housing at least partly defines a fluid path between the first end of the second housing and the second end thereof. In addition, the DDU includes a reductant delivery unit (RDU) housing in which the fuel injector and the attachment assembly are disposed. The RDU housing is configured to directly attach to an exhaust pipe of a vehicle.

In an example embodiment, the attachment assembly further includes a seat fixedly disposed within the second housing; and an attachment assembly needle movably disposed within the second housing and including a first end portion, the attachment assembly needle movable between a first position in which the first end portion of the attachment assembly needle contacts and provides a sealing engagement with the seat of the attachment assembly so as to prevent fluid from exiting the second housing through the second end thereof, and a second position in which the first end portion of the attachment assembly needle extends outwardly from the second end of the second housing and is spaced from the seat of the attachment assembly. A spring member is disposed within the second housing and coupled to the attachment assembly needle so as to bias the attachment assembly needle towards the first position thereof and prevent fluid in the second housing from exiting the second housing through the second end thereof. In this way, when the valve assembly is in the open state, fluid in the fuel injector exits the fuel injector from the fluid outlet thereof and enters the fluid path of the second housing under pressure so as to cause the attachment assembly needle to overcome the bias of the spring member and move to the second position for allowing the fluid to exit the second housing from the second end thereof. When the valve assembly is in the closed state, fluid in the fuel injector is prevented from passing into the fluid path of the second housing so as to cause the spring member to bias the attachment assembly needle to move to the second position and prevent the fluid from exiting the second housing from the second end thereof.

In an example embodiment, the fuel injector and the attachment assembly are dimensioned to have a combined profile which matches a profile of an injector of an existing RDU, and the RDU housing is a housing for the existing RDU.

In an example embodiment, the DDU includes at least one gasket disposed downstream of the attachment assembly, relative to a direction of fluid flow through the injector assembly. The at least one gasket at least partly thermally isolates the fuel injector and the attachment assembly from the exhaust pipe. The DDU may further include a flange having a sidewall into which an end portion of the DDU housing is disposed, the flange including an inner surface extending in a radial direction, wherein the at least one gasket includes a first gasket disposed between a downstream end portion of the attachment assembly and the inner surface of the flange. In addition, the flange may further include a downstream-facing outer surface disposed in the radial direction of the DDU, and the DDU may further include a second gasket disposed between the outer surface of the flange and a boss of the exhaust pipe of the vehicle.

In an example embodiment, the DDU is an actively cooled DDU and the RDU housing includes a coolant inlet for receiving a coolant, a coolant outlet for returning a coolant, and a coolant jacket in fluid communication with the coolant inlet and the coolant outlet. The coolant jacket surrounds the attachment assembly and at least part of the fuel injector.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a side view of a fluid injector according to an example embodiment;

FIG. 2 is a partial cross sectional side view of the fluid injector of FIG. 1;

FIG. 3 is a detailed cross sectional view of an attachment assembly of the fluid injector of FIGS. 1 and 2;

FIG. 4 is a perspective view of an air cooled DDU having therein the fluid injector of FIGS. 1-3, according to an another example embodiment;

FIG. 5 is a side view of the air cooled DDU of FIG. 4;

FIG. 6 is a partial cross sectional view of the DDU of FIG. 4;

FIG. 7 is a side view of a liquid cooled DDU having therein the fluid injector of FIGS. 1-3, according to another example embodiment; and

FIG. 8 is a partial cross sectional view of the DDU of FIG. 7.

DETAILED DESCRIPTION

The following description of the example embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

Example embodiments of the present disclosure are directed to an injector assembly which utilizes an existing inward-opening fluid injector, such as a fuel injector, as the metering device of the injector assembly, and an attachment assembly which is connected to the fuel outlet of the fuel injector and which includes an outward opening valve. The resulting injector assembly is suitable as an injector for a DDU (i.e., a DDU injector) or for other applications in which a fluid injector is susceptible to coking. For reasons of simplicity, the injector assembly will be described hereinbelow for use as a DDU injector for a diesel dosing system (DDS).

Referring now to the FIGS. 1 and 2, there is shown an injector assembly 10 which is resistant to coking. According to an example embodiment, injector assembly 10 includes a fluid injector 12 and an attachment assembly 14 attached to a downstream end of fluid injector 12. Fluid injector 12 is an existing fluid injector, such as an existing fuel injector. In one example embodiment, fluid injector 12 is a gasoline based port fuel injector. Fluid injector 12 is an inward opening fluid injector and/or has a valve assembly which is inward opening. In the example embodiments, fluid injector 12 is utilized in injector assembly 10 as the metering device for controlling the flow of fluid exiting injector assembly 10. In the context of injection assembly 10 forming a DDU injector, fluid injector 12 meters the flow of diesel fuel from fluid injector 12 for injection into the exhaust pipe of a diesel engine. Use of an existing, relatively low cost injector, such as an existing fuel injector and particularly an existing gasoline based port fuel injector, provides a simplified, inexpensive and more robust injector assembly 10.

It is understood that fluid injector 12 may be any of a number of different inward opening fluid/fuel injectors. In general terms, fluid injector 12 includes components and/or parts commonly found in fluid injectors: a housing or body 15; a fluid inlet 16 in which fluid is received from a fluid source; and a fluid outlet 18 which provides a metered flow of fluid exiting fluid injector 2. Housing 15 may at least partly define a fluid path between fluid inlet 16 and fluid outlet 18. Fluid injector 12 may further include an actuator unit 20 disposed within housing 15. In an example embodiment, actuator unit 20 includes a coil 20A, pole piece 20B and a movable armature 20C disposed in proximity to coil 20A. Energizing coil 20A, such as by passing a current through the coil, causes armature 20C to move in an axial direction within housing 15 towards pole piece 20B. Fluid injector 12 may further include a valve assembly 22 having an axially movable valve needle 24 with one end coupled to armature 20C and a second end; and a valve seat 26 disposed at or near the fluid outlet 18 of fluid injector 12. Valve needle 24 is movable between a first (closed) position in which the second end of valve needle 24 sealingly contacts valve seat 26 so that fluid in fluid injector 12 is prevented from exiting through fluid outlet 18 (shown in FIGS. 2 and 3), and a second (open) position in which the second end of valve needle 24 is moved in an upstream direction, relative to the flow of fluid through fluid injector 12, so that the second end of valve needle 24 is spaced apart from valve seat 26 to allow fluid in the fluid path of fluid injector 12 to exit through fluid outlet 18. A spring (not shown) is disposed in the housing 15 and coupled to armature 20C to bias the armature away from pole piece 20B, which biases the valve needle 24 to the first (closed) position. Energizing coil 20A causes armature 20C to move so that the valve needle 24 moves to the second (open) position. In this way, the inward opening valve assembly 22 is controlled via coil 20A to open and close the valve assembly to selectively provide a metered amount of fluid from fluid injector 12.

Best seen in FIG. 2 and, in an enlarged view, in FIG. 3, attachment assembly 14 includes a housing having a first (upstream) end 30 and a second (downstream) end 32. Attachment assembly 14 further includes, disposed in housing or body 34, an outward opening valve subassembly including a needle 36, seat 38, return spring 40 and spring stop 42. Needle 36 and seat 38 each includes a sealing surface which when engaged with each other, provides a seal which prevents fluid in housing 34 from exiting through second end 32 thereof. Spring stop 42 includes a pocket 42A defined along one axial side thereof which receives an end portion of spring 40. A second end portion of spring 40 engages with seat 38. An axial end portion of needle 36 is connected to spring stop 42, and a central portion of needle 36 is disposed within spring 40. The second axial end portion of needle 36 is connected to spring stop 42. Spring 40 biases needle 36 so that needle 36 sealingly engages with seat 38. Needle 36 and seat 38 are dimensioned so that fluid exiting housing 34 has a largely cone shaped pattern. Once needle 36, seat 38, spring 40 and spring stop 42 are connected to each other in this way to form the valve subassembly, the valve subassembly is inserted into and fixed within housing 34. In particular, seat 38 is welded within the inner surface of housing 34, such as with a laser weld. The components of the valve subassembly—needle 36, seat 38, spring 40 and spring stop 42—may be constructed from stainless steel or comparable materials.

As mentioned, attachment assembly 14 is connected to the downstream end of fluid injector 12 near fluid outlet 18 thereof. In one embodiment, first end 30 of housing 34 of attachment assembly 14 is laser welded to the downstream end of housing 15 of fluid injector 12. The connected end of housing 34 may be configured so that the connected end is press fit into the inner surface of the end of housing 15 before the laser welding. Alternatively, attachment assembly 14 may be attached to fluid injector 12 using other techniques, such as crimping, threaded engagement, brazing, etc.

With attachment assembly 14 connected to fluid injector 12, injector assembly 10 is formed as an outward opening injector, with fluid injector 12 utilized as the metering valve of injector assembly 10. Fluid injector 12 controls the flow of fluid through injector assembly 10, with the fluid discharged from injector assembly 10 having a spray pattern defined by attachment assembly 14 and particularly the dimensions of needle 36 and seat 38 of attachment assembly 14.

In use, fluid which entered the fluid path of fluid injector 12 via fluid inlet 16 is prevented from exiting the fluid path through fluid outlet 18 when coil 20A of fluid injector 12 is de-energized, which allows for the spring within fluid injector 12 to bias valve needle 24 so as to contact and sealingly engage with valve seat 26, thereby placing valve assembly 22 in the closed state. With no fluid build-up or pressure within housing 34 of attachment assembly 14 due to valve assembly 22 being closed, spring 40 urges needle 36 against seat 38 so as to prevent fluid from exiting attachment assembly 14 through second end 32. In this state, injector assembly 10 is closed. When coil 20A is energized, armature 20C is urged in the upstream direction towards fluid inlet 16, thereby separating the end of valve needle 24 from valve seat 26 so as to allow the fluid in the fluid path of fluid injector 12 to exit fluid injector 12 through fluid outlet 18. Such exiting fluid enters housing 34 of attachment assembly 14 which causes fluid pressure in housing 34 to build against spring stop 42 and/or needle 36 until the pressure overcomes the bias forces on needle 36 by spring 40 and causes needle 36 and spring stop 42 to move downwardly so that needle 36 separates from seat 38 and allows fluid in attachment assembly 14 and fluid injector 12 to exit injector assembly 10 via seat 38. In this state, injector assembly 10 is in the open position. The exiting fluid has a spray pattern dependent upon the dimensions of needle 36 and seat 38.

With injector assembly 10 using fluid injector 12 as a metering device and attachment assembly 14 providing a flow pattern for fluid exiting attachment assembly 14, injector assembly 10 utilizes an existing fluid injector having an inward opening injector valve and attachment assembly 14 to result in an integrated, unitary injector assembly. Attachment assembly 14 having an outward opening valve subassembly formed by needle 36, seat 38, spring 40 and spring stop 42 advantageously prevents coking at or around seat 38 and prevents needle 36 from sticking thereto. Injector assembly 10 finds use in applications in which injectors are susceptible to coking and/or valves sticking, such as DDUs.

As mentioned above, injector assembly 10 utilizes an existing, lower cost fuel injector as fluid injector 12, which lowers the cost of manufacturing injector assembly 10 and results in a robust fluid injector design. In accordance with another example embodiment, injector assembly 10 is utilized in a DDU as a DDU injector. In the embodiment, the profile (and/or outer dimensions) of injector assembly 10 matches or nearly matches the profile (and/or outer dimensions) of a fluid injector used in existing reductant delivery units (RDUs) of a selective catalytic reduction (SCR) system. As a result of having the same or similar profile/outer dimensions of an existing RDU injector, a DDU having injector assembly 10 may utilize an existing RDU housing of the existing RDU fluid injector. Using, with injector assembly 10, the existing RDU housing with proven thermal protection of the RDU fluid injector results in a further lowering of design and manufacturing costs and a faster time to market. With some DDUs having smaller sales volumes than RDU sales volumes, utilizing existing injector and RDU technology in DDU designs provides significant cost advantages for DDU manufacturers.

In example embodiment, fluid injector 12 is an existing gasoline based port fuel injector. The port fuel injector has an existing counterpart injector having an extended tip which is used as an existing RDU injector of an existing RDU SCR system. Among other things, the extended tip of the counterpart RDU fuel injector provided greater distance of some components of the injector from the heated exhaust path of a vehicle and resulted in an injector having a greater length. In the example embodiment, attachment assembly 14 is sized so that when combined with the gasoline based port fuel injector used for fluid injector 12, the total length and other dimensions defining the profile of injector assembly 10 matches the total length and other dimensions defining the profile of the counterpart RDU injector. By utilizing an existing port fuel injector and sizing the attachment assembly 14 so that injector assembly 10 has the same dimensions as an existing RDU injector, the RDU housing of the existing RDU injector may be used as the housing for a DDU having injector assembly 10.

FIGS. 4-6 illustrate a passive or air cooled DDU 100 according to an example embodiment. DDU 100 includes injector assembly 10 as the DDU injector as described above, with fluid injector 12 being an existing gasoline port fuel injector having an RDU injector counterpart with an elongated tip. DDU 100 allows for direct mounting of injector assembly 10 to the exhaust pipe of a vehicle. FIGS. 4-6 illustrate DDU 100 having DDU housing formed as an upper housing 102 and a lower housing 104. The DDU housing is the housing of an existing RDU. DDU 100 further includes a diesel fuel inlet 106 for receiving diesel fuel which passes through fluid injector 12 and attachment assembly 14 and is selectively discharged from the downstream end of attachment assembly 14. Both upper housing 102 and lower housing 104 includes a plurality of through-holes defined along the housings for allowing air to pass though the housings and regulate temperatures internal to the housings. Injector assembly 10 is disposed in an interior carrier 106. Upper housing 102 and lower housing 104 are connected to carrier 106, such as by folding tangs of an end portion of lower housing 104 so as to surround and clamp in place end portions of upper housing 102 and carrier 106.

DDU 100 further includes an injector flange 108 which receives therein the downstream end of lower housing 104. Specifically, flange 108 includes a sidewall 108A which defines an inner space in which the downstream end of lower housing 104 is disposed. Injector flange 108 includes internal surface structure, generally indicated at 110, that defines a flange outlet 112 that delivers fluid into an exhaust boss 114 of an exhaust flow path. Thus, as shown in FIG. 6, the flange 108 is coupled to an end of the exhaust boss 114 with the flange outlet 112 communicating with a bore of the boss 114. The bore communicates with the exhaust flow path.

The internal surface structure 110 of flange 108 also includes a largely frusto-conical surface that is joined with at least one radius surface. In the embodiment, the conical surface defines the open end of the flange 38 and is joined with the radius surface, with the radius surface being joined directly with a gasket shelf surface 116 of the flange 108. The gasket shelf surface 116 is disposed generally perpendicular with respect to a longitudinal axis of the injector assembly 10.

DDU 100 further includes an isolating gasket 118 which rests on the gasket shelf surface 62 to seal the flange 108 with respect to the carrier 106, and a second isolating gasket 120 disposed between a downstream end of flange 108 and an upstream end of exhaust boss 114. Both isolating gaskets 118 and 120 serve to thermally isolate injector assembly 10 from high temperatures of the exhaust stream in the exhaust flow path of the vehicle, by blocking heat flow paths from the exhaust pipe through exhaust boss 114 and flange 108 to injector assembly 10. DDU 100 thus uses isolating gaskets 118 and 120 as well as cooling airflow around DDU 100 to keep temperatures of injector assembly 10 from high temperatures which may damage injector assembly 10.

Passively cooled DDU 100 is utilized for applications in which mounting locations along the exhaust pipe have lower temperatures and available cooling airflow. For mounting locations where the ambient temperature and the exhaust gas temperatures are higher, an actively cooled DDU may be used. Referring to FIGS. 7 and 8, there is shown an actively cooled DDU 200 according to another example embodiment. DDU 200 includes injector assembly 10 disposed in an existing RDU housing 201. DDU 200 is actively cooled by passing coolant around injector assembly 10 so as to maintain temperatures thereof within a desirable temperature range. Housing 201 includes a diesel fuel inlet 202 for receiving diesel fuel which flows into injector assembly 10 for being selectively sprayed into the exhaust flow path of the corresponding vehicle. Housing 201 further includes a coolant inlet 204 for receiving coolant from a coolant source, and a coolant outlet 206 for returning coolant to the coolant source for recirculation. Housing 201 further includes a coolant jacket 208 which is fluidly coupled to coolant inlet 204 and coolant outlet 206. Coolant jacket 208 is disposed around injector assembly 10, and particularly around the portions of injector assembly 10 closest to the exhaust pipe, such as attachment assembly 14 and the downstream portion of fluid injector 12. As shown in FIG. 8, coolant jacket 208 extends to or nearly to the bottom or downstream end of attachment assembly 14. Actively cooled DDU 200 includes a V-clamp mount for mounting DDU 200 directly to the vehicle exhaust pipe.

It is understood that features of passively cooled DDU 100 and actively cooled DDU 200 may be utilized for providing further thermal protection to injector assembly 10. For example, DDU 200 may include isolating gaskets 118 and/or 120 to disrupt any heat transfer path from the exhaust pipe to injector assembly 10.

The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention. 

What is claimed is:
 1. A diesel dosing unit (DDU), comprising: a fluid injector assembly, comprising: a fluid injector comprising a first housing, a fluid inlet disposed at a first end of the first housing for receiving fluid, a fluid outlet disposed at a second end of the first housing for exiting fluid from the first housing, the first housing defining at least in part a fluid path through the first housing between the fluid inlet and the fluid outlet, the fluid injector further including an actuator unit and a valve assembly operably coupled thereto for selectively discharging fluid in the fluid path from the fluid outlet when the valve assembly is in an open state and for preventing fluid in the fluid path from exiting the fluid outlet when the valve assembly is in a closed state; and an attachment assembly, comprising: a second housing having a first end attached or attachable to the second end of the first housing and a second end, the second housing at least partly defining a fluid path between the first end of the second housing and the second end thereof; a seat fixedly disposed within the second housing; an attachment assembly needle movably disposed within the second housing and including a first end portion, the attachment assembly needle movable between a first position in which the first end portion of the attachment assembly needle contacts and provides a sealing engagement with the seat of the attachment assembly so as to prevent fluid from exiting the second housing through the second end thereof, and a second position in which the first end portion of the attachment assembly needle extends outwardly from the second end of the second housing and is spaced from the seat of the attachment assembly; and a spring member disposed within the second housing and coupled to the attachment assembly needle so as to bias the attachment assembly needle towards the first position thereof and prevent fluid in the second housing from exiting the second housing through the second end thereof, wherein when the valve assembly is in the open state, fluid in the fluid injector exits the fluid injector from the fluid outlet thereof and enters the fluid path of the second housing under pressure so as to cause the attachment assembly needle to overcome the bias of the spring member and move to the second position for allowing the fluid to exit the second housing from the second end thereof, and when the valve assembly is in the closed state, fluid in the fluid injector is prevented from passing into the fluid path of the second housing so as to cause the spring member to bias the attachment assembly needle to move to the second position and prevent the fluid from exiting the second housing from the second end thereof; and a DDU housing in which the injector assembly is disposed, the DDU housing is configured to directly attach to an exhaust pipe of a vehicle.
 2. The DDU of claim 1, wherein the DDU housing is a housing of a reductant delivery unit (RDU).
 3. The DDU of claim 2, wherein the injector assembly is dimensioned to have a profile which matches a profile of an injector of an existing RDU, and the DDU housing is a housing for the existing RDU.
 4. The DDU of claim 3, wherein the DDU is a passively cooled DDU and the DDU housing includes a plurality of through-holes defined along the DDU housing.
 5. The DDU of claim 3, wherein the DDU is a passively cooled DDU and the DDU includes at least one gasket disposed downstream of the attachment assembly, relative to a direction of fluid flow through the injector assembly, the at least one gasket thermally isolating the injector assembly.
 6. The DDU of claim 5, further comprising a flange having a sidewall into which an end portion of the DDU housing is disposed, the flange including an inner surface extending in a radial direction, wherein the at least one gasket comprises a first gasket disposed between a downstream end portion of the attachment assembly and the inner surface of the flange.
 7. The DDU of claim 6, wherein the flange further includes an outer surface disposed in the radial direction of the DDU, and the DDU further comprises a second gasket disposed between the outer surface of the flange and a boss of the exhaust pipe of the vehicle.
 8. The DDU of claim 3, wherein the DDU is an actively cooled DDU and the DDU housing includes a coolant inlet for receiving a coolant, a coolant outlet for returning a coolant, and a coolant jacket in fluid communication with the coolant inlet and the coolant outlet, the coolant jacket defining a space around at a least a portion of the injector assembly.
 9. The DDU of claim 3, wherein the fluid injector comprises a gasoline port fuel injector, the gasoline port fuel injector and the attachment assembly defining a profile which matches the profile of the injector of the existing RDU.
 10. A diesel dosing unit (DDU), comprising: a fuel injector comprising a first housing, a fluid inlet disposed at a first end of the first housing for receiving fluid, a fluid outlet disposed at a second end of the first housing for exiting fluid from the first housing, the first housing defining at least in part a fluid path through the first housing between the fluid inlet and the fluid outlet, the fuel injector further including an actuator unit and a valve assembly operably coupled thereto for selectively discharging fluid in the fluid path from the fluid outlet when the valve assembly is in an open state and for preventing fluid in the fluid path from exiting the fluid outlet when the valve assembly is in a closed state; an attachment assembly comprising a second housing having a first end attached or attachable to the second end of the first housing and a second end, the second housing at least partly defining a fluid path between the first end of the second housing and the second end thereof; and a reductant delivery unit (RDU) housing in which the fuel injector and the attachment assembly are disposed, the RDU housing configured to directly attach to an exhaust pipe of a vehicle.
 11. The DDU of claim 10, wherein the attachment assembly further comprises: a seat fixedly disposed within the second housing; an attachment assembly needle movably disposed within the second housing and including a first end portion, the attachment assembly needle movable between a first position in which the first end portion of the attachment assembly needle contacts and provides a sealing engagement with the seat of the attachment assembly so as to prevent fluid from exiting the second housing through the second end thereof, and a second position in which the first end portion of the attachment assembly needle extends outwardly from the second end of the second housing and is spaced from the seat of the attachment assembly; and a spring member disposed within the second housing and coupled to the attachment assembly needle so as to bias the attachment assembly needle towards the first position thereof and prevent fluid in the second housing from exiting the second housing through the second end thereof, wherein when the valve assembly is in the open state, fluid in the fuel injector exits the fuel injector from the fluid outlet thereof and enters the fluid path of the second housing under pressure so as to cause the attachment assembly needle to overcome the bias of the spring member and move to the second position for allowing the fluid to exit the second housing from the second end thereof, and when the valve assembly is in the closed state, fluid in the fuel injector is prevented from passing into the fluid path of the second housing so as to cause the spring member to bias the attachment assembly needle to move to the second position and prevent the fluid from exiting the second housing from the second end thereof.
 12. The DDU of claim 10, wherein the fuel injector and the attachment assembly are dimensioned to have a combined profile which matches a profile of an injector of an existing RDU, and the RDU housing is a housing of the existing RDU.
 13. The DDU of claim 10, wherein the DDU includes at least one gasket disposed downstream of the attachment assembly, relative to a direction of fluid flow through the injector assembly, the at least one gasket at least partly thermally isolating the fuel injector and the attachment assembly from the exhaust pipe.
 14. The DDU of claim 13, further comprising a flange having a sidewall into which an end portion of the DDU housing is disposed, the flange including an inner surface extending in a radial direction, wherein the at least one gasket comprises a first gasket disposed between a downstream end portion of the attachment assembly and the inner surface of the flange.
 15. The DDU of claim 14, wherein the flange further includes an outer surface disposed in the radial direction of the DDU, and the DDU further comprises a second gasket disposed between the outer surface of the flange and a boss of the exhaust pipe of the vehicle.
 16. The DDU of claim 10, wherein the DDU is an actively cooled DDU and the RDU housing includes a coolant inlet for receiving a coolant, a coolant outlet for returning a coolant, and a coolant jacket in fluid communication with the coolant inlet and the coolant outlet, the coolant jacket surrounding the attachment assembly and at least part of the fuel injector. 